Curl resistant dust collecting mats



United States Patent Ofiice 3,306,808 Patented Feb. 28, 1967 3,306,808 CURL RESISTANT DUST COLLECTING MATS Dewey T. Thompson and William T. Fincher, La Grange, Ga., assignors to Callaway Mills Company, La Grange, Ga., a corporation of Georgia No Drawing. Filed Nov. 22, 1963, Ser. No. 325,750 30 Claims. (Cl. 161-66) This application is a continuation-in-part of our copen-ding application Serial No. 304,644, filed August 26, 1963.

This invention relates to a method for preventing curling of mats of the type used for removing dust and the like from the shoes of persons entering buildings and offices, which mats are subjected to repeated laundering and reconditioning.

In many office buildings, schools, hospitals, homes, factories, machine shops, warehouses, and the like, a problem arises due to the carrying of moisture, dust, filings, and other debris on the shoes of persons going from one area to other areas. Dust mats of various kinds have been employed with varying success, but tend to become unsightly and unsanitary. In recent times, a mat that has good washability has been developed. These mats are made preferably from cellulosic and cotton duck backing and yarn by the familiar tufting technique. After the tufting, the loops are anchored to the duck backing to prevent reveling by coating with a rubber latex which is then dried and vulcanized or cured. The curing step is carried out at elevated temperatures conventionally employed but at temperatures below that at which the cotton fiber is damaged. This not only serves to fix the loops in place during washing and use, but provides an antiskid surface which keeps the mat from sliding when walked upon.

The pile of the mat is provided with a dust collecting oil which is used in an amount tending to absorb or hold dust and other debris from the shoes of a person who walks across it, or who wipes his shoes thereon before entering the area which is desired to protect.

The dust collecting oil is a high-boiling petroleum oil having a high flash point and other properties as set forth later herein. The proportions used are such that it does not stain the shoes, yet tends to retain the dirt, usually being in the range of about 0.075 to about 1.0 ounce per square foot. This will vary with the fabric, but should be such that excessive tracking off of the oil does not occur. Optimum oil content will be such that there is little or not noticeable track off.

After a period of service which will depend upon the amount of traffic over it, as well as the amount of dirt collected, the mat is laundered in any type of industrial laundry wheel. Being made of cellulosics, preferably of cotton, the mats are readily laundered by familiar techniques which need not be described in great detail. They are washed at 140 F.200 F. water temperature, using soaps or detergents, alkalies, water softeners, etc. They are then rinsed and dried, for example, in high temperature gas driers, steam driers or electric driers.

The mats are usually provided on a rental basis by a service company which replaces dirty mats with clean ones and launders and reconditions the dirty mats. In the course of laundering, the dust collecting oil is removed along with soil, and must be replaced before the mat is returned to service.

It has been found that upon repeated washing and reconditioning the mats do not lay flat, but tend to curl upward at the corners and edges. This creates a safety hazard because people tend to trip over them. Some mats may curl within a few washings, while with others the tendency develops only after more extensive washings.

The cause of the curling has not been well understood. However, we have found that several factors enter into the problem. One of these is the type of elastomer employed. We have discovered that coating the mat with a nitrile-diene rubber latex having from about 20% to about 60% nitrile to about 80% to about 40% (based on the rubber content of the latex) of a conjugated diene having from 4 to 6 carbon atoms per molecule of diene monomer, have less tendency to curl than mats coated with other types of natural or synthetic rubbers. The preferred rubber is a copolymer of acrylonitrile and butadiene. In general, as the nitrile content of the rubber is increased, the tendency to curl decreases, but even so increasing the nitrile content does not in and of itself completely solve the curling problem.

Another factor influencing curling resides in the potential shrinkage of the duck backing. If the backing is desized, scored and subjected to compressive shrinkage (Sanforizing), or otherwise preshrunk, before the tufting operation, the resultant mat is more resistant to curling. Thus, washing the duct backing to constant dimensions (0.0% potential shrinkage) before tufting and coating with latex products a mat of considerably improved stability. This represents the maximum benefit to be obtained from this factor alone. The degree of preshrinking of the backing determines the degree of benefit to be realized from this step alone. Less severe preshrinking will result in curling tendencies of the finished mat lying somewhere between those made from the greige backing I and those made from one of zero potential shrinkage.

The shrinking can also be carried out after the tufting operation but before the latex backing is applied and cured. This is generally more effective than preshrinking the duck backing before tufting, but it is also more expensive.

The potential shrinkage of the greige goods from the loom is normally about 12-14% as measured in the warpwise direction. The potential shrinkage is determined on the griege goods by measuringthe difference in dimension between the goods from the loom and that after being shrunk to constant dimension. This is determined by subjecting the goods to repeated laundering in a commercial type wash wheel at 200 F. with the normal amount of detergent. The fabric is rinsed, extracted and dried. The goods are then measured. The cycle is repeated until constant dimensions are obtained. The potential shrinkage of the backing should not be above about 12.5% and is preferably between zero and about The method used herein was based on a wash formulati-on of 14 ounces sodium metasilicate, 40 cc. of a neutral,

nonionic synthetic detergent of the alkylphenolethylene oxide condensate type, in 2025 gallons of water. The fabric was washed 20 minutes at 200 F. and then rinsed with water at -160 F. four times and once with cold water. It was extracted for two minutes and dried in an electric household tumbler dried for one hour. The dried fabric sample was measured, and the cycle repeated until constant measurements were obtained.

A further factor in the curling problem is the petroleum dust collecting oil used for conditioning the mat originally, and reconditioning it after launderingp We have found that the proper selection of a petroleum dust collecting oil having a boiling point above about 500 F., a specific gravity between 0.85 and 0.95, and a minimum aniline point which is determined by the potential shrinkageremaining in the duck backing and the percentage of the nitrile component of the elastomeric copolyrner 3 This relationship, which involves all three factors is somewhat difficult to express quantitatively so as to embrace every possible variable. However, specific examples at the extremes and some intermediate points of the shrinkage range will indicate the minimum aniline point requirement for use with a given elastomer. From this, one skilled in the art will known how to practice the invention under varying conditions.

, In thecase of the following examples, the latices were 'copolymers of acrylonitrile and butadiene. Elastomers having three acrylonitrile contents were selected, namely 22%, 33% and 45%, respectively. The latices contained the usual antioxidants, antifoarning agents, titanium dioxide, Zinc oxide, and accelerators such as Z-mercaptobenzothiazole and zinc diethyldithiocarbamate. Just before the latex is applied to the mat a vulcanizing agent, usually sulfur, is added to the latex. Materials suitable for these purposes are well known in the prior art. The viscosity of the latex may be varied to a consistency best suited for coating the mats by use of thickeners or thinners. In the case of the examples given below, the viscosity was adjusted to about 4000 cps, as determined with LVF spindle No. 4 at 6 rpm. on a Brookfield viscometer. The properties of the petroleum dust collecting oils 1 As determined by ASTM Method D-1160 at 10mm. Hg and converted to 760 mm. It represents the initial boiling point, not the entire distillationrange.

The proportion of latex solids applied to the mat may range from about to about 15 ounces per square yard. About 10.5 to 11 ounces per square yard were used in the following examples. The latex was cured with sulfur as the vulcanizing agent, at about 290 F. for 15 minutes drying and curing time.

Mats having satisfactory resistance to curling may be produced by correlating the factors discussed above. Backing fabric, potential shrinkage, .elastomer composition and minimum aniline point of the petroleum dust collecting oil for illustrative mats embodying the invention are set forth in the following Table 2.

TAB LE 2 Potential Shrinkage of Duck Backing Minimum Aniline Point of the Oil Percent Acrylonitrile in Copolymer: 180

leum dust collecting oils may be suitable for use under specific conditions. These can be selected to effect conditioning and reconditioning of the mats and to overcome the curling problem accompanying repeated laundering, where it is advantageous to alter the copolymer composi tion or the degree of potential shrinkage or both.

The petroleum dust collecting oil may be applied to the laundered fabric in several ways. The oil itself may be sprayed onto the pile of the mat after it has been washed and dried. Alternatively, it may be rolled on with a paint roller. The oil could be applied as an aque-- ous emulsion or as a solution in a volatile solvent. This would entail evaporating the water or the solvent from the mat before use.

However, a particularly convenient and preferred method is to add the oil containing a suitable emulsifying agent to the water in the wash wheel to form an emulsion. The fabric absorbs the oil from the dilute water suspen sion so that little or none is lost. The oil is added in the proportions mentioned before.

The foregoing examples are by way of illustration and should not be construed as limiting the invention to the exact procedure described therein.

We claim:

1. A dust collecting mat comprising a plurality of cel= lulosic yarns tufted to one side of a cellulosic fabric hav ing a potential shrinkage from 0 to about 12.5%, the other side of said fabric having an elastomeric backing comprising about 20% to 60% acrylonitrile copolymer= ized with about 40% to 80% of a conjugated diene haw ing from 4 to 6 carbon atoms per molecule of diene mon omer, said tufted yarns having absorbed thereon a petro= leum dust collecting oil having an aniline point above about 230 F., a specific gravity between about 0.85 and about 0.95, and a boiling point above about 500 F.

2. A dust collecting mat according to claim 1 wherein the conjugated diene is butadiene.

3. A dust collecting mat according to claim 1 wherein the cellulosic fabric is cotton duck and has been preshrunk to a potential shrinkage between 0 and 5%.

4. A dust collecting mat according to claim 1 wherein the quantity of absorbed petroleum dust collecting oil is in the range of 0.075 to 1.0 ounce per square foot surface area of the mat.

5. A dust collecting mat comprising a plurality of cellulosic yarns tufted to one side of a cellulosic fabric having a potential shrinkage from 0 to about 12.5%, the

other side of said fabric having an elastomeric backing comprising about 33% to 60% acrylonitrile copolymerized with about 40% to 67% of a conjugated diene hav ing from 4 to 6 carbon atoms per molecule of diene monomer, said tufted yarns having absorbed thereon a petroleum dust collecting oil having an aniline point above about 180 F., a specific gravity between about 0.85 and about 0.95, and a boiling point above about 500 F.

6. A dust collecting mat according to claim 5 wherein the conjugated diene is butadiene.

7. A dust collecting mat according to claim 5 wherein the cellulosic fabric is cotton duck and has been preshrunk to a potential shinkage between 0 and 5%.

8. A dust collecting mat according to claim 5 wherein the quantity of absorbed petroleum dust collecting oil is in the range of 0.075 to 1.0 ounce per square foot surface area of the mat.

9. A dust collecting mat comprising a plurality of cellulosic yarns tufted to one side of the cellulosic fabric having a potential shrinkage from 0 to about 12.5%, the other side of said fabric having an elastomeric backing comprising about 45% to 60% acrylonitrile copolymerized with about 40% to 55% of a conjugated diene having from 4 to 6 carbon atoms per molecule of diene monomer, said tufted yarns having absorbed thereon a petroleum dust collecting oil having an aniline point above about F., a specific gravity between about 0.85 and 0.95, and a boiling point above about 500 F.

10. A dust collecting mat according to claim 9 Wherein the conjugated diene is butadiene.

11. A dust collecting mat according to claim 9 wherein the cellulosic fabric is cotton duck and has been preshrunk to a potential shrinkage between and 12. A dust collecting mat according to claim 9 wherein the quantity of absorbed petroleum dust collecting oil is in the range of 0.075 to 1.0 ounce per square foot surface area of the mat.

13. A dust collecting mat comprising a plurality of cellulosic yarns tufted to one side of the cellulosic fabric having a potential shrinkage from 0 to about 4.5%, the other side of said fabric having an elastomeric backing comprising about 20% to 60% acrylonitrile copolymerized with about 40% to 80% of a conjugated diene having from 4 to 6 carbon atoms per molecule of diene monomer, said tufted yarns having absorbed thereon a petroleum dust collecting oil having an aniline point above about 180 F., a specific gravity between about 0.85 and about 0.95, and a boiling point above about 500 F.

14. A dust collecting mat according to claim 13' wherein the conjugated diene is butadiene and the cellulosic fabric is cotton duck.

15. A dust collecting mat according to claim 13 wherein the quantity of absorbed petroleum dust collecting oil is in the range of 0.075 to 1.0 ounce per square foot surface area of the mat.

16. A dust collecting mat comprising a plurality of cellulosic yarns tufted to one side of a cellulosic fabric having a potential shrinkage from 0 to about 4.5%, the other side of said fabric having an elastomeric backing comprising about 33% to 60% acrylonitrile copolymerized with about 40% to 67% of a conjugated diene having from 4 to 6 carbon atoms per molecule of diene monomer, said tufted yarns having absorbed thereon a petroleum dust collecting oil having an aniline point above about 135 F., a specific gravity between about 0.85 and 0.95, and a boiling point above about 500 F.

17. A dust collecting mat according to claim 16 wherein the conjugated diene is butadiene and the cellulosic fabric is cotton duck.

18. A dust collecting mat according to claim 16 wherein the quantity of absorbed petroleum dust collecting oil is in the range of 0.075 to 1.0 ounce per square foot surface area of the mat.

19. A dust collecting mat comprising a plurality of cellulosic yarns tufted to one side of a cellulosic fabric having a potential shrinkage from 0 to about 4.5%, the other side of said fabric having an elastomeric backing comprising about 45% to 60% acrylonitrile copolymerized with about 40% to 55% of a conjugated diene having from 4 to 6 carbon atoms per molecule of diene monomer, said tufted yarns having absorbed thereon a petroleum dust collecting oil having an aniline point above about 75 F., a specific gravity between about 0.85 and 0.95, and a boiling point above about 500 F.

20. A dust collecting mat according to claim 19 Wherein the cellulosic fabirc is cotton duck and the conjugated diene is butadiene.

2-1. A dust collecting mat according to claim 19 wherein the quantity of absorbed petroleum dust collecting oil is in the range of 0.075 to 1.0 ounce per square foot surface area of the mat.

22. A dust collecting mat comprising a plurality of cellulosic yarns tufted to one side of a cellulosic fabric having about zero potential shrinkage, the other side of said fabric having an elastomeric backing comprising about 22% to 60% acrylonitrile copolymerized with about 40% to 78% of a conjugated diene having from 4 to 6 carbon atoms per molecule of diene monomer, said tufted yarns having absorbed thereon a petroleum dust collecting oil having an aniline point above about 160 F., a specific gravity between about 0.85 and 0.95, and a boiling point above about 500 F.

23. A dust collecting mat according to claim 22 wherein the cellulosic fabric is cotton duck and the conjugated diene is butadiene.

24. A dust collecting mat according to claim 22 wherein the quantity of absorbed petroleum dust collecting oil is in the range of 0.075 to 1.0 ounce per square foot surface area of the mat.

25. A dust collecting mat comprising a plurality of cellulosic yarns tufted to one side of a cellulosic fabric having about zero potential shrinkage, the other side of said fabric having an elastomeric backing comprising about 33% to 60% acrylonitrile copolymerized with about 40% to 67% of a conjugated diene having from 4 to 6 carbon atoms per molecule of diene monomer, said tufted yarns having absorbed thereon a petroleum dust collecting oil having an aniline point above about F., a specific gravity between about 0.85 and 0.95, and a boiling point above about 500 F.

26. A dust collecting mat according to claim 25 wherein the cellulosic fabric is cotton duck and the conjugated diene is butadiene.

27. A dust collecting mat according to claim 25 Wherein the quantity of absorbed petroleum dust collecting oil is in the range of 0.075 to 1.0 ounce per square foot surface area of the mat.

28. A dust collecting mat comprising a plurality of cellulosic yarns tufted to one side of a cellulosic fabric having about zero potential shrinkage, the other side of said fabric having an elastomeric backing comprising about 45% to 60% acrylonitrile copolymerized with about 40% to 55% of a conjugated diene having from 4 to 6 carbon atoms per molecule of diene monomer, said tufted yarns having absorbed thereon a petroleum dust collecting oil having an aniline point above about 50 F., a specific gravity between about 0.85 and 0.95, and a boiling point above about 500 F.

29. A dust collecting mat according to claim 28 wherein the cellulosic fabric is cotton duck and the conjugated diene is butadiene.

30. A dust collecting mat according to claim 28 wherein the quantity of absorbed petroleum dust collecting oil is in the range of 0.075 to 1.0 ounce per square foot surface area of the mat.

References Cited by the Examiner UNITED STATES PATENTS 2,033,170 3/1936 Alt et al. 11768 3,007,808 11/1961 Smith 11768 ALEXANDER WYMAN, Primary Examiner.

R. H. CRISS, Assistant Examiner. 

1. A DUST COLLECTING MAT COMPRISING A PLURALITY OF CELULOSIC YARNS TUFTED TO ONE SIDE OF A CELLULOSIC FABRIC HAVING A POTENTIAL SHRINKAGE FROM 0 TO ABOUT 12.5%, THE OTHER SIDE OF SAID FABRIC HAVING AN ELASTOMERIC BACKING COMPRISING ABOUT 20% TO 60% ACRYLONITRILE COPOLYMERIZED WITH ABOUT 40% TO 80% OF A CONJUGATED DIENE HAVING FROM 4 TO 6 CARBON ATOMS PER MOLECULE OF DIENE MONOMER, SAID TUFTED YARNS HAVING ABSORBED THEREON A PETROLEUM, DUST COLLECTING OIL HAVING AN ANILINE POINT ABOVE ABOUT 230*F., A SPECIFIC GRAVEITY BETWEEN ABOUT 0.85 AND ABOUT 0.95, AND A BOILING POINT ABOVE ABOUT 500*F. 